My New Dog is Over-Protective with Me

I got a 9-month-old boxer/lab female pup 10 days ago. She's very intelligent and easily trained/obedient, but she guards me too much. From the second I brought her home, she immediately became overly attached to me and guarded me from my family and everyone else. I have been using treats or affection for positive reinforcement when she is social/calm and when I'm training her. Negative reinforcement with a verbal "no" or "stop it" and ignoring her, pushing her off of me, or walking away. She is no longer protecting me from my family 98% of the time. She's gotten better but it is still an issue when I take her out in public. A dog trainer saw her territorial behavior when we were at a dog park and she suggested I use scent conditioning with a spray bottle with a 50:50 mix of apple vinegar and water. Now she's friendly when we are walking and first arrive somewhere, but as soon as she settles in or I sit somewhere, she begins to ferociously guard me against the world. The methods I've tried don't help much once she starts doing this. I have to walk away for her to stop, but once I stop moving she settles in and begins to guard again. She does not guard resources, isn't jealous when I pet other dogs or interact with my family, and is submissive to me. I would really appreciate some help, and sorry for the long post.